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            <h1 style="display: none">strace 跟踪进程中的系统调用</h1>
            
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              <p>strace常用来跟踪进程执行时的系统调用和所接收的信号。 在Linux世界，进程不能直接访问硬件设备，当进程需要访问硬件设备(比如读取磁盘文件，接收网络数据等等)时，必须由用户态模式切换至内核态模式，通过系统调用访问硬件设备。strace可以跟踪到一个进程产生的系统调用,包括参数，返回值，执行消耗的时间。</p>
<h1 id="1-输出参数含义"><a href="#1-输出参数含义" class="headerlink" title="1. 输出参数含义"></a>1. 输出参数含义</h1><p>每一行都是一条系统调用，等号左边是系统调用的函数名及其参数，右边是该调用的返回值。 strace 显示这些调用的参数并返回符号形式的值。strace 从内核接收信息，而且不需要以任何特殊的方式来构建内核。</p>
<figure class="highlight stylus"><table><tr><td class="gutter"><div class="code-wrapper"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></div></td><td class="code"><pre><code class="hljs stylus"><span class="hljs-variable">$strace</span> cat /dev/null<br><span class="hljs-function"><span class="hljs-title">execve</span><span class="hljs-params">(<span class="hljs-string">&quot;/bin/cat&quot;</span>, [<span class="hljs-string">&quot;cat&quot;</span>, <span class="hljs-string">&quot;/dev/null&quot;</span>], [/* <span class="hljs-number">22</span> vars */])</span></span> = <span class="hljs-number">0</span><br><span class="hljs-function"><span class="hljs-title">brk</span><span class="hljs-params">(<span class="hljs-number">0</span>)</span></span>                                  = <span class="hljs-number">0</span>xab1000<br><span class="hljs-function"><span class="hljs-title">access</span><span class="hljs-params">(<span class="hljs-string">&quot;/etc/ld.so.nohwcap&quot;</span>, F_OK)</span></span>      = -<span class="hljs-number">1</span> ENOENT (No such file or directory)<br><span class="hljs-function"><span class="hljs-title">mmap</span><span class="hljs-params">(NULL, <span class="hljs-number">8192</span>, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -<span class="hljs-number">1</span>, <span class="hljs-number">0</span>)</span></span> = <span class="hljs-number">0</span>x7f29379a7000<br><span class="hljs-function"><span class="hljs-title">access</span><span class="hljs-params">(<span class="hljs-string">&quot;/etc/ld.so.preload&quot;</span>, R_OK)</span></span>      = -<span class="hljs-number">1</span> ENOENT (No such file or directory)<br>...<br></code></pre></td></tr></table></figure>

<h1 id="2-参数"><a href="#2-参数" class="headerlink" title="2. 参数"></a>2. 参数</h1><figure class="highlight mercury"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br></pre></td><td class="code"><pre><code class="hljs mercury">-c 统计每一系统调用的所执行的时间,次数和出错的次数等.<br>-d 输出strace关于标准错误的调试信息.<br>-f 跟踪由fork调用所产生的子进程.<br>-ff 如果提供-o filename,则所有进程的跟踪结果输出到相应的filename.pid中,pid是各进程的进程号.<br>-F 尝试跟踪vfork调用.在-f时,vfork不被跟踪.<br>-h 输出简要的帮助信息.<br>-i 输出系统调用的入口指针.<br>-q 禁止输出关于脱离的消息.<br>-r 打印出相对时间关于,,每一个系统调用.<br>-t 在输出中的每一行前加上时间信息.<br>-tt 在输出中的每一行前加上时间信息,微秒级.<br>-ttt 微秒级输出,以秒了表示时间.<br>-T 显示每一调用所耗的时间.<br>-v 输出所有的系统调用.一些调用关于环境变量,状态,输入输出等调用由于使用频繁,默认不输出.<br>-V 输出strace的版本信息.<br>-x 以十六进制形式输出非标准字符串<br>-xx 所有字符串以十六进制形式输出.<br>-a column<br>设置返回值的输出位置.默认 为<span class="hljs-number">40</span>.<br>-e expr<br>	指定一个表达式,用来控制如何跟踪.格式如下:<br>		[qualifier<span class="hljs-built_in">=</span>][!]value1[,value2]...<br>		qualifier只能是 <span class="hljs-keyword">trace</span>,abbrev,verbose,raw,signal,read,write其中之一.value是用来限定的符号或数字.默认的 qualifier是 <span class="hljs-keyword">trace</span>.感叹号是否定符号.例如:<br>-eopen等价于 -e <span class="hljs-keyword">trace</span><span class="hljs-built_in">=</span>open,表示只跟踪open调用.而-etrace!<span class="hljs-built_in">=</span>open表示跟踪除了open以外的其他调用.有两个特殊的符号 <span class="hljs-built_in">all</span> 和 none.<br>注意有些shell使用!来执行历史记录里的命令,所以要使用\\.<br>-e <span class="hljs-keyword">trace</span><span class="hljs-built_in">=</span>set<br>只跟踪指定的系统 调用.例如:-e <span class="hljs-keyword">trace</span><span class="hljs-built_in">=</span>open,close,rean,write表示只跟踪这四个系统调用.默认的为set<span class="hljs-built_in">=</span><span class="hljs-built_in">all</span>.<br>-e <span class="hljs-keyword">trace</span><span class="hljs-built_in">=</span>file<br>只跟踪有关文件操作的系统调用.<br>-e <span class="hljs-keyword">trace</span><span class="hljs-built_in">=</span>process<br>只跟踪有关进程控制的系统调用.<br>-e <span class="hljs-keyword">trace</span><span class="hljs-built_in">=</span>network<br>跟踪与网络有关的所有系统调用.<br>-e strace<span class="hljs-built_in">=</span>signal<br>跟踪所有与系统信号有关的 系统调用<br>-e <span class="hljs-keyword">trace</span><span class="hljs-built_in">=</span>ipc<br>跟踪所有与进程通讯有关的系统调用<br>-e abbrev<span class="hljs-built_in">=</span>set<br>设定 strace输出的系统调用的结果集.-v 等与 abbrev<span class="hljs-built_in">=</span>none.默认为abbrev<span class="hljs-built_in">=</span><span class="hljs-built_in">all</span>.<br>-e raw<span class="hljs-built_in">=</span>set<br>将指 定的系统调用的参数以十六进制显示.<br>-e signal<span class="hljs-built_in">=</span>set<br>指定跟踪的系统信号.默认为<span class="hljs-built_in">all</span>.如 signal<span class="hljs-built_in">=</span>!SIGIO(或者signal<span class="hljs-built_in">=</span>!io),表示不跟踪SIGIO信号.<br>-e read<span class="hljs-built_in">=</span>set<br>输出从指定文件中读出 的数据.例如:<br>-e read<span class="hljs-built_in">=</span><span class="hljs-number">3</span>,<span class="hljs-number">5</span><br>-e write<span class="hljs-built_in">=</span>set<br>输出写入到指定文件中的数据.<br>-o filename<br>将strace的输出写入文件filename<br>-p pid<br>跟踪指定的进程pid.<br>-s strsize<br>指定输出的字符串的最大长度.默认为<span class="hljs-number">32</span>.文件名一直全部输出.<br>-u username<br>以username 的UID和GID执行被跟踪的命令<br></code></pre></td></tr></table></figure>

<h1 id="3-命令实例"><a href="#3-命令实例" class="headerlink" title="3. 命令实例"></a>3. 命令实例</h1><h2 id="3-1-跟踪可执行程序"><a href="#3-1-跟踪可执行程序" class="headerlink" title="3.1 跟踪可执行程序"></a>3.1 跟踪可执行程序</h2><figure class="highlight powershell"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><code class="hljs powershell">strace <span class="hljs-operator">-f</span> <span class="hljs-operator">-F</span> <span class="hljs-literal">-o</span> ~/straceout.txt myserver<br></code></pre></td></tr></table></figure>
<p>-f -F选项告诉strace同时跟踪fork和vfork出来的进程，-o选项把所有strace输出写到~/straceout.txt里 面，myserver是要启动和调试的程序。</p>
<h2 id="3-2-跟踪服务程序"><a href="#3-2-跟踪服务程序" class="headerlink" title="3.2 跟踪服务程序"></a>3.2 跟踪服务程序</h2><figure class="highlight apache"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><code class="hljs apache"><span class="hljs-attribute">strace</span> -o output.txt -T -tt -e trace=<span class="hljs-literal">all</span> -p <span class="hljs-number">28979</span><br></code></pre></td></tr></table></figure>
<p>跟踪28979进程的所有系统调用（-e trace=all），并统计系统调用的花费时间，以及开始时间（并以可视化的时分秒格式显示），最后将记录结果存在output.txt文件里面。</p>

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